With the rapid development of communications technologies, increasingly higher requirements are imposed on mobile terminals such as mobile phones. In order to satisfy growing demands for communications, a multi-mode terminal technology, capable of supporting two or more types of modes at the same time, has been developed so far. In the multi-mode terminal technology, a multi-mode single-standby terminal means that when a terminal device works, only a set of radio frequency channels work for a certain mode at the same time; and a multi-mode multi-standby terminal means that when a terminal device works, multiple sets of radio frequency channels corresponding to multiple modes work at the same time. A most common application of multi-mode multi-standby is multi-mode dual-standby.
However, a multi-mode dual-standby technology has not been stipulated by a protocol standard so far, and therefore, a multi-mode dual-standby terminal is generally required to be separately registered for a CS (Circuit Switched, circuit switched) domain and a PS (Packet Switched, packet switched) domain, instead of co-registration. When the multi-mode dual-standby terminal roams out of network coverage of a communications operator (such as China Mobile), the terminal generally can work in only one of the CS domain and the PS domain. When the terminal roams out of the network coverage of China Mobile, for example, only the CS domain is available, at this time, a roaming user can use only modes camping on the CS domain such as GSM, TDS-CDMA, and WCDMA, but cannot use modes such as LTE and WCDMA in the PS domain through inter-system interoperations such as co-registration, CSFB and multi-mode single-standby.